Discus b spins from thermal; aft CG and incomplete type check-out

The pilot of a Discus b was fatally injured in an unrecovered spin near Buttwil; aircraft destroyed. After aerotow release at ~1 300 m MSL the glider joined a thermal beneath another glider, then departed into a spin from ~1 100 m MSL; no recovery attempt was observed before it struck a hangar roof, flipped and came to rest inverted on a second roof. The pilot had ~157 h total with only 1:18 h on type over three flights and no record of spin training. The CG sat near the aft limit (cockpit minimum load 85 kg, pilot 75 kg fully equipped), and the club familiarisation programme was completed unsupervised after the first flight.

1. Aerotow from Buttwil: The pilot took an aerotow from RWY 34 at Buttwil for a local soaring flight in a single-seat Discus b. The pilot held a German glider licence with ~157 h total on gliders accumulated over 15 years; recent experience was almost entirely on a Ka 6 wooden glider. On the Discus b he had three flights totalling 1:18 h before this flight.
2. Aft CG and low time on type: Fully equipped the pilot weighed 75 kg; the cockpit placard for this airframe required a minimum cockpit load of 85 kg (other Discus b of the club required 75 kg). With 4.4 kg of fixed nose ballast the CG lay near the aft limit — about 2% inside the rearmost permitted position. The flight manual warns that at aft CG full rudder in a stalled state will provoke a spin. There was no record in the pilot's career of any practical spin training on a glider.
3. Familiarisation flown unsupervised: The club familiarisation programme called for three flights supervised by an instructor or experienced pilot. The pilot had completed one supervised flight on a different Discus b airframe (16 min), then made two short unsupervised flights on the accident airframe on a day when no instructor was rostered. No completion entry had been made in his logbook. The accident flight was the fourth flight on type and was also unsupervised.
4. Thermalling below another glider: The pilot announced release after about four minutes on tow and released at ~1 300 m MSL, roughly 700 m AGL. He joined a thermal beneath another glider that was circling at ~1 600 m MSL and was observed circling at ~1 100–1 150 m MSL.
5. Unintended spin from ~1 100 m MSL: Shortly after, the higher pilot saw the Discus b enter a spin from ~1 100 m MSL (roughly 500 m AGL). Likely cause was an inadvertent excursion below the published 68 km/h straight-flight stall speed — markedly higher than that of the Ka 6 the pilot was current on — combined with the aft CG. Standard recovery from the spin in this type loses 50–80 m, so recovery from the entry altitude was feasible.
6. No recovery attempt observed: Witnesses observed several spin rotations with no visible attempt at recovery. The airspeed indicator showed slightly above 130 km/h at impact and the altimeter froze at 640 m, consistent with continued autorotation to ground contact.
7. Roof impact; pilot fatally injured: The glider's nose struck the roof of an industrial building in the village, the airframe somersaulted and came to rest inverted on a second roof. The pilot was ejected on impact and fatally injured; the aircraft was destroyed. The investigation found no pre-existing technical defects and no medical pre-conditions. The probable cause was an unintended spin that was not recovered before ground impact; the aft CG, very limited experience on type, absence of spin training, and an incomplete and unsupervised type familiarisation contributed.